Postpartum Thyroiditis

Abstract

Postpartum thyroiditis is a common thyroid disorder that presents during the first postpartum year. It is the occurrence of either transient hyperthyroidism, transient hypothyroidism, or transient hyperthyroidism followed by transient hypothyroidism (Fig. 1). Most, but not all, women are euthyroid 1 yr postpartum. Postpartum thyroiditis is an exacerbation of an underlying autoimmune thyroiditis, aggravated by the immunological rebound that follows the partial immunosuppression of pregnancy (1–3). Women who express human leukocyte antigen haplotypes DR-3, DR-4, and DR-5 have an increased risk for postpartum thyroiditis. In women who develop postpartum thyroiditis, CD4+/CD8+ and CD4 + 2H4+ ratios are elevated throughout pregnancy and the postpartum (4). Histologically, thyroid aspirates reveal either a lymphocytic infiltrate or diffuse destruction, changes similar to those seen in both Hashimoto’s thyroiditis (2, 3, 5) and painless sporadic silent thyroiditis (6). In essence, the immunological rebound that follows the end of pregnancy precipitates the clinical expression of Hashimoto’s disease, which before pregnancy was clinically silent (2). The time course and pattern of thyroid function tests in postpartum thyroiditis. Patients who experience the hypothyroid phase of postpartum thyroiditis can either return to the euthyroid state by 1 yr postpartum or remain hypothyroid. The prevalence of postpartum thyroiditis varies widely. Although geographic differences account for some of the variance, a critical factor has been methodological differences in study design. Not only has every prevalence study used a different methodology, but few studies performed their initial screen during pregnancy. Consequently, some of the women diagnosed with postpartum thyroiditis may have had preexisting Hashimoto’s disease. In calculating the prevalence rate of postpartum thyroiditis, only the 13 studies that met the following criteria were included: 1) follow-up extended until a minimum of 5 months postpartum, and 2) patients were evaluated on at least two distinct time points postpartum. All 13 studies were prospective, with screening for postpartum thyroiditis performed at predetermined time periods, dictated by study protocol. The prevalence of postpartum thyroiditis ranges between 1.1% and 16.7% (1, 3, 5, 7–15), with a mean prevalence rate of 7.2%. In individuals with type 1 diabetes mellitus, the prevalence rate triples (16, 17). Specifically, in the New York metropolitan area, the general prevalence of postpartum thyroiditis of 8.8% increased to 25% in women with type 1 diabetes (16). The increased prevalence of postpartum thyroiditis in women with type 1 diabetes mellitus is not surprising, because both are autoimmune disorders. Furthermore, prior studies have demonstrated an increased prevalence of thyroid antibodies in individuals with type 1 diabetes. Postmiscarriage thyroiditis also occurs, but no prevalence data are available (18, 19). Furthermore, as in type 1 diabetes, I postulate that women with other autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, and scleroderma would have an increased prevalence of postpartum thyroiditis. However, no studies to date have evaluated the prevalence of postpartum thyroiditis in these disorders. The recurrence rate in postpartum thyroiditis is high. Seventy percent of women with a prior episode of postpartum thyroiditis develop a recurrence in the subsequent pregnancy. Antithyroid peroxidase-positive women, who did not develop postpartum thyroiditis during an initial pregnancy, have a 25% chance of having postpartum thyroiditis after the next pregnancy. In contrast, women who had neither antithyroid peroxidase nor postpartum thyroiditis during an initial pregnancy, do not develop postpartum thyroiditis in future pregnancies (20). A total of 371 episodes of postpartum thyroiditis are described in the 13 prevalence studies. The most common presentation, found in 43% of the cases, was hypothyroidism without preceding hyperthyroidism. Hyperthyroidism, by itself, was present in 32% of the reported cases. Least common, comprising 25% of the episodes, was hyperthyroidism, followed by hypothyroidism. Symptoms can occur during either phase of postpartum thyroiditis. The hyperthyroid symptoms are typically subtle. It is often diagnosed retrospectively, with the symptoms recognized at the time of diagnosis of hypothyroidism. The hypothyroid phase can also go unrecognized. Consequently, an undetermined percentage of women with postpartum thyroiditis remain undiagnosed. This is due to a woman experiencing minimal or no symptoms, the attribution of symptoms to the demands of child rearing, or a lack of recognition of the symptoms by the physician. The hyperthyroid phase of postpartum thyroiditis occurs between 2 and 10 months postpartum. Most commonly, it presents at 3 months. Symptoms more common in women with hyperthyroid postpartum thyroiditis include palpit